Update Documentaion. Populate new instance of acoustid db.

[eleksir]

I encounter with problem initialising db.

I presume, nowdays acoustid-servers uses triple-db configuration: acoustid_app, acoustid_fingerprint, acoustid_ingest. Also it requires musicbrainz db. But in README.md there is no words about it. How to create this (relatively) new format of database schema? and how to perform initial database population with new format of data?

Also no traces of scripts/acoustid_sync.py that is called by admin/run-sync-acoustid.sh, so there is unknown how to perform syncs with https://data.acoustid.org/ in correct way.